1. Field of the Invention
The invention relates to a wood planing machine, more particularly to a wood planing machine provided with an automatic chain tensioner device.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional wood planing machine 10 is shown to include an elongated machine base 14, left and right pairs of posts 16, a cutter carriage 12, vertical left and right threaded rods 11, two sprockets 111, an endless transmission chain 13, and a chain tensioner device.
As illustrated, the machine base 14 has opposed left and right mounting short sides 140, and opposed feed-in and take-out long sides 141. The left and right pairs of posts 16 are fixed on the machine base 14 at the left and right mounting short sides 141, respectively. The cutter carriage 12 is disposed above the machine base 14, and has opposite end portions mounted respectively, vertically and movably on the left and right pairs of posts 16. The threaded rods 11 are mounted respectively and rotatably on the left and right mounting short sides 140 of the machine base 14 such that the threaded rods 11 are disposed respectively between the left and right pairs of posts 16, and extend threadedly through the opposite end portions of the cutter carriage 12. The sprockets 111 are disposed below the machine base 14 and are sleeved respectively and fixedly on lower end portions of the left and right threaded rods 11. The chain 13 is disposed below the machine base 14 and engages the sprockets 111 so as to rotate the left and right threaded rods 11 synchronously for moving the cutter carriage 12 along the posts 16 when the threaded rods 11 rotate on the machine base, thereby adjusting the height of the carriage 12 relative to the machine base 14. The chain 13 has front and rear chain sections 131,132 disposed respectively adjacent to the feed-in and take-out long sides 141 of the machine base 14.
The chain tensioner device includes an elongated horizontal rod 15 disposed below and pivoted to the machine base 14 by means of a pivot bolt 152 in such a manner that the rod 15 is located between the front and rear chain sections of the chain 13, and a pair of gears 151 which are mounted respectively and rotatably on two opposite end portions of the rod 15 and which engage respectively the front and rear chain sections 131,132 under tension when one of the threaded rods 11 is rotated.
One disadvantage that results from the use of the aforesaid conventional wood planing machine resides in that, in order to provide the tensioning effect, the rod 15 is locked on the machine base 14 by the pivot bolt 152, which may loosen due to long term use, thereby adversely affecting the chain tensioning ability.